Keeping warm can be classified into two concepts. One is to prevent heat from body from being emitted to the outside, and the other is to actively applying heat to body from the outside. The former uses a thermal insulation method for insulating heat from body by air layer of fabrics, a method for using an infrared-reflecting material for not emitting radiant heat from body to the outside of clothing, and a material for absorbing body radiation energy. The latter uses electronic heating materials, chemical-reaction heat-warming materials, and solar-cell storage-heat materials in covered yarns.
In the thermal insulation method using the air layer, the thickness of fabrics increased to reduce activity. The rest of above-mentioned methods are not widely available because laundering or durability is reduced.
In the meanwhile, thermal conductivity is defined as the quantity of heat transmitted through a unit thickness in a direction normal to a surface of unit area due to a unit temperature gradient under steady state conditions and when the heat transfer is dependent only on the temperature gradient. The thermal conductivity of isotropic material is scalar, and thermal conductivity of anisotropic material is tensor. In specifically, metal has high thermal conductivity due to heat conductivity of free electron and Wiedemann-Franz Law is completed between thermal conductivity and electric conductivity. Thermal conductivity is affected by density, specific heat, and viscosity. For instance, linen fibers with high thermal conductivity are cooling fibers, and wool with low thermal conductivity is warm fibers.
Korean laid-open Patent No. 1991-3210 discloses the manufacturing method of the coated fabric in which heat insulation nature and deodorant are excellent. Concretely, the above patent relates to a manufacturing method of coating fabric for forming a coating layer by a mixture of particle obtained by sintering and grinding polyurethane solution of a solid of 30±1% using dimethyl form-amide as a solvent, microcline of 20% to 80%, beryllium oxide of 5% to 20%, zinc oxide of 5% to 15%, tin oxide of 5% to 15% and Zeolite A on a surface of a synthetic fabric. In this manufacturing method, the coating layer is formed on the fabric, so that there are disadvantages in washing and durability.
In addition, international publication No. WO 2002/34988 discloses a thermal textile made at least in part with conductive yarns for the purpose of generating heat from an electrical power source. The textile comprises has at least one conducting yarn and heater yarns have a positive temperature coefficient. This patent has disadvantages in that additional power generating structure is required, and coating compatibility is reduced.